This invention relates to a process of removing phosgene from off gases by contacting the off gases with aqueous alkali metal hydroxide solutions containing tertiary amines.
It is known from U.S. Pat. No. 2,430,861 that hexamethylenetetramine can neutralize phosgene in a phenolic oil solution.
It is known from U.S. Pat. Nos. 3,376,113; 3,411,867 and 3,789,580 that phosgene can be removed from gases by using activated alumina.
It is also known from U.S. Pat. Nos. 3,314,753 and 4,301,126 that phosgene can be removed from gases by using activated carbon.
The use of aqueous caustic solutions containing ammonia to remove phosgene from off gases is taught by U.S. Pat. No. 4,064,218.
The present invention is superior to the known prior art in that the use of beds of activated alumina or carbon with their need for regeneration is eliminated. The known use of caustic-ammonia scrubbing is much less efficient than the present invention.